Carrier Lifetimes in a III-V-N Intermediate Band Semiconductor

TL;DR

This study measures carrier lifetimes in GaPAsN, revealing short lifetimes that hinder solar cell efficiency, and highlights the need for material improvements for practical applications.

Contribution

First measurement of carrier dynamics in GaPAsN using transient absorption spectroscopy, providing insights into recombination processes relevant for solar cell development.

Findings

Conduction band electron lifetime is approximately 23 ps.

Intermediate band exhibits bimolecular recombination with a specific rate.

Carrier lifetimes are too short for efficient solar power conversion.

Abstract

We have used transient absorption spectroscopy to measure carrier lifetimes in the multiband band semiconductor GaPAsN. These measurements probe the electron populations in the conduction band, intermediate band and valance band as a function of time after an excitation pulse. Following photoexcitation of GaP0.32As0.67N0.01 we find that the electron population in the conduction band decays exponentially with a time constant 23ps. The electron population in the intermediate band exhibits bimolecular recombination with recombination constant r = 2 10^-8 cm-3/s. In our experiment an optical pump pulse excited electrons from the valance band to the intermediate and conduction bands, and the change in interband absorption due to absorption saturation and induced absorption was probed with a delayed white light pulse. We modeled the optical properties of our samples using the band anti-crossing model to extract carrier densities as a function of time. These results indicate that the minority carrier lifetimes are too short for efficient solar power conversion and that improvements in material quality will be required for practical applications of GaPAsN based intermediate band solar cells.